Bismuth Sulfite Agar

EMD Cat. No. 1.05418.0500
500 g


Selective agar introduced by WILSON and BLAIR (1927, 1931) for the isolation and differentiation of Salmonella typhi and other salmonellae.

This medium complies with the recommendations of the United States Pharmacopeia XXIII (1995) and the recommendations of the APHA (1992) for foodstuff examinations.







Mode of Action Preparation
Experimental Procedure and Evaluation Quality Control
Typical Composition (g/liter) Literature
Picture/Image


Mode of Action
 Brilliant green and bismuth largely inhibit the accompanying bacterial flora. Colonies of H2-S-positive salmonellae exhibit blackening due to the formation of iron sulfide. Reduction of bismuth ions to metallic bismuth produces a metallic lustre around the colonies (McCOY 1962).

Typical Composition (g/liter)
 Meat extract 5.0; peptone from meat 10.0; D(+)glucose 5.0; di-sodium hydrogen phosphate 4.0; iron(III) sulfate 0.3; brilliant green 0.025; bismuth sulfite indicator 8.0; agar-agar 15.0.


Preparation
 Suspend 47.5 g in 1 liter of purified water, mix the resulting precipitate to give a uniform suspension, pour plates to give thick layers (25 ml).

  •   Do not autoclave.

    pH: 7.6 ± 0.2 at 25 °C.

    The prepared medium is turbid and green in color.
  •   The freshly prepared medium is strongly inhibitory and is thus especially suitable for heavily contaminated samples. The metallic lustre of the colonies usually only appears after 48 hours on incubation. After 4 days storage at 4 °C the inhibitory action of the medium is not as strong and it should then be used for less heavily contaminated specimens; in this case the metallic lustre appears after a shorter period of incubation.


    Experimental Procedure and Evaluation
     Inoculate by thinly spreading the sample or material from an enriched culture on the surface of the medium.
    Incubation: up to about 48 hours at 35°C aerobically.

    Salmonella colonies often display blackening after 18 hours of incubation, the metallic sheen appears several hours later depending on the age of the medium.

    Appearance of Colonies
         		Microorganisms
    Black centre, light edges surrounded by a black precipitate with metallic sheen (so-called rabbit's or fish-eye)
         		Salmonella with the exception of S. parathyphi A. and S. pullorum
    Small, green to brown, sometimes mucoid
         		Coliform bacteria, Serratia, Proteus and others


    Quality control

    Test strains
    		 Growth
         		Black centre
         		Metallic sheen
    Salmonella typhimurium ATCC 14028
         		good / very good
         		+
         		+
    Salmonella choleraesius ATCC 13322
         		good / very good
         		+
         		+
    Salmonella enteritidis NCTC 5188
         		good / very good
         		+
         		+
    Salmonella arizonae ATCC 13314
         		good / very good
         		+
         		+/-
    Salmonella aboni NCTC 6017
         		good / very good
         		+
         		+
    Escherichia coli ATCC 25922
         		poor / fair
         		-
    Proteus mirabilis ATCC 29906
         		good / very good
         		±
    Shigella sonnei ATCC 11060
         		none / poor

    Staphylococcus aureus ATCC 25923
         		none / poor

    Bacillus cereus ATCC 11778
         		none

    Literature

    American Public Health Association: Compendium of Methods for the Microbiological Examination of Foods. 3rd ed., 1992.
     McCOY, J.H.: The isolation of Salmonellae. J. Appl. Bact., 25; 213-224 (1962).
     United States Pharmacopoeia XXIII, Chapter "Microbial Limit Tests", 1995.
     WILSON, W.J., a BLAIR, E.M. McV.: Use of glucose bismuth sulfite iron medium for the isolation of Bacillus typhosus and Bacillus proteus. J. Hyg., 26; 374-391 (1927).
     WILSON, W.J., a. BLAIR, E.M. McV.: Further experience of the bismuth sulfite media in the isolation of Bacillus typhosus and Bacillus paratyphosus B from faeces, sewage and water. J. Hyg. 31; 138-161 (1931).


    Salmonella typhimurium



    © 2002 Merck KGaA, Darmstadt, Germany